Trane furnace E09: Open inducer limit switch or condensate pressure switch
E09 means either the inducer limit switch or the condensate pressure switch is open. On a condensing furnace this is most often a blocked condensate drain.
Applies to: Trane and American Standard S9V2 two-stage condensing variable speed gas furnaces with a seven-segment integrated furnace control display, per Installer's Guide 18-CE01D1-1E-EN.
What it means
A condensing furnace produces water as a by-product, several litres a day in cold weather, and it has to go somewhere. The condensate pressure switch exists to stop the furnace running when it cannot drain. Trane proves this switch together with the inducer limit switch at the very start of the sequence, before the inducer is even energised, by sending 24 volts out the HLO terminal and watching the ILI input. If either is open the furnace does not start at all. The reason this code is worth understanding is that the fix is frequently simple and frequently ignored — a blocked drain, a full trap, a kinked hose. A furnace that will not run in January because of a plugged drain line is a common and entirely preventable call.
Most common causes
- A blocked or slow condensate drain line.
- A condensate trap that is full, dirty or dry.
- A kinked, cracked or disconnected condensate hose.
- A condensate pump that has failed or is full.
- An open inducer limit switch, which is the less common of the two causes.
- Freezing in a condensate line that runs through an unheated space.
How to diagnose it
- Look for standing water in or around the furnace, and check whether the condensate drain is running freely.
- If there is a condensate pump, check whether it is full or has stopped.
- In very cold weather, consider whether the drain line passes through an unheated space and could be frozen.
- Note whether the furnace does nothing at all when it calls for heat — this fault stops it before the inducer starts.
How to fix it
- Clearing a blocked condensate drain is often the entire repair, and the drain should be cleaned annually.
- A frozen line needs the freezing addressed, not just thawed, or it recurs.
- The switches themselves are technician work.
- Do not bypass the condensate switch. A condensing furnace that cannot drain will put water where it does not belong.
Notes
This is one of the more preventable codes on the site. Annual condensate drain cleaning removes most of the causes before they become a no-heat call in the coldest week of the year.
Related
- E3.2 — Open pressure switch, first stage
- Which Trane code system you have — Trane furnaces use either flash codes or a seven-segment display, and they share no numbering
All codes for this manufacturer
Trane and American Standard furnace flash codes — every code, with what differs between models.
What the fix costs
Most E09 calls resolve on the condensate side, where the price floor is zero — a cleared drain or an emptied trap is often the entire repair. The technician versions price off the repair guide: a pressure switch at $150–400, with its standing advice applying doubly here — find the blockage before replacing the switch that detected it. The inducer limit switch end of the code is the less common one and lands as ordinary diagnostic-plus-part work; the guide lists inducer-side repairs at $300–900 when the motor itself is implicated. The preventive version — an annual condensate drain cleaning at a maintenance visit — undercuts all of them. More codes like this across brands: inducer motor codes.
DIY or call a pro
The drain side of this code is the most homeowner-friendly territory in the Trane fault table. Standing water, a full condensate pump, a visibly slow or blocked drain line, a trap that needs emptying, a hose kinked behind the cabinet — all checkable, and mostly fixable without going anywhere near the combustion side of the furnace. In freezing weather, add the question of whether the drain crosses unheated space. The switches themselves stay off-limits: both are safety interlocks, proven before the inducer even starts, and bypassing the condensate switch just relocates the water into the furnace. If the drain runs clear and the code stays, the switch work is the visit.
What this looks like
From the outside, this usually shows up as the furnace heats then trips out on high limit — that walkthrough covers what to check in order, and when it stops being a homeowner job.
This can also show up as water pooling around the furnace or a blocked condensate line — that page covers where the water comes from and what to check first.